C# Calculation and Adding a symbol

Question

Hey guys...

 

 

This is how my form looks:

http://i.imgur.com/ZbSCQ0P.png

 

In my project, the items that I add with the prices in basket, add together, and I have the price for all of them together, displayed in the text box. 

 

http://i.imgur.com/RyE6j08.png

 

What I want to do now, is writing a number into 'Payment Cash text box' and when I press 'Calculate Change button' I want the 'Total Price' number to be taken away from the 'Payment Cash' number and the number that is left, to be displayed in the 'Total Change text box'

 

Also if the number in 'Payment Cash text box' would be smaller than 'Total Price'  I would like if the number displayed would show how much more money you need to pay.

 

For example:

 

The 'Total Price' is £100 and the 'Payment Cash' is £80, I would like the 'Total Change text box" to show - £20.

 

 If that's not possible, then at least it would be nice, if a message would pop out, that says how much I need to pay more.

 

 

The last thing I want to ask, is how could I add  the  '£' symbol into the prices.

 

 

string[] Men = new string[3];

string[] Women = new string[5];

string[] Children = new string[4];

double[] MenPrice = new double[3];

double[] WomenPrice = new double[5];

double[] ChildrenPrice = new double[4];

 

I used double[] for the prices, and for double[] I don't think I can use anything else than numbers.

 

 

Sorry for my bad English, and I will be really thankfull for any help.